Process and apparatus for supplying heat to molten material



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C. T. PATTRSf'N 'PROCESS AND PPARATUS FOR SUPPLYLNG HEAT TO MOLTENMATERAL Sept. 28

Sheat Filed March G Sept. 28 1926. 1,60,703

c. T. PATTERSON PROCESS AND APPARATUS FOR SUPPLYING HEAT TO MOLTENMATERIAL Filed March 6. 1925 P. Sheets-Sheet '2 Patented Sept. 28, 1926.

UNITED STATES PATENT OFFICE. I

CLARENCE T. PATTERSON, OF SYRACUSE, NEW YORK, ASSIGNOR TO THE SOLVAYPROCESS COMPANY, F SOLVAY, NEW YORK, A CORPORATION OE NEW YORK.

PROCESS AND APPARATUS FOR SUPPLYING HEAT TO MOLTEN MATERIAL.

Application led March 6, 1925.

My invention relates to electric resistance furnaces in which thematerial to be heated forms the resistance element and particularly tofurnaces ofthis type for materials such as metallic salts whose heatcapacity and heat conductivity are relatively poor compared with that-ofmetals and metallic substances. In apparatus designed for this purposeconsiderable difficulty has been l0 experienced in bringing to a uniformstate of fusion or maintaining at the uniform desired temperature theentire amount of material contained within the furnace. The heat becomeslocalized in the immediate vicinity of the electrodes so that only asmall portion of the material will be acted upon, and this portion maybe heated too intensely leading to vaporization, in some cases, or suchintense local heating ma electrodes of the furnace to ecome destroyed. Apossible solution of this difficulty is either to decrease the furnacedimensions or to enlarge and shape the electrodes so as to produce auniform current flow throughout the entire material to be treated. Sucha solution is not ractical because of the relatively large oss of heatfrom the syst/em via the relatively large electrodes and furnace walls.The current consumption becomes uneconomical.

The object of my invention is to provide a process and apparatus ofsuchcharacter f that the danger of local overheating will be avoided andyet the entire mass of material will be economically maintained at theproptemperature at all points. It has been ouiid that a certain minimumrelation between the current and the area of contact of the electrodeswith the material, i. e., current density at the surface of contactbetween the electrodes and the molten material, will produce the properheating action, this minimum current density depending on the nature ofthe particular material under treatment. When this relation issatisfied, movements are set up in the fusion mass such that all the'required heat can be supplied without local over-heatin and this heatdistributed so that a relatively uniform and the desired temperature ismaintained throughout the entire mass. While the current -density shouldnot fall below a certain figure, depending on the nature of suchmaterial, it must not exceed a certain upper lim-y it, since otherwisedangerous and destructive cause thev Serial No. 13,648.

local heating effects may result. In carrying out this invention theshape of the electrodes is of importance, as well as the preservation ofa proper relation between the current and the area. of contact of theelectrodes with the fused material.

In the accompanying drawings, I have illustrated in diagrammatic fashiontwo types of apparatus suitable for carrying out the present invention.Fig. 1 is a plan view of one of such form of apparatus, Fig. 2 is avertical section on line 2--2 of Fig. 1, Fig. 3 is a vertical section ofa secondform of furnace embodying this invention, and Fig. 4 illustratesupon an enlarged scale an electrode suitable for use in the improvedfurnace. Fig. 5 is a partly diagrammatic and partly sectional view of acommercial furnace and its associated equipment. Fig. 6 is a plan viewof the furnace part of F ig. 5.

The particular apparatus which has been selected for the purpose ofillustrating theinvention and which is shown in the drawings, is of a'character particularly adapted for the continuous production of fusedsoda ash or soda ash-sodium hydroxid mixtures. A is the furnace body,lwhich may be made of steel boiler plate insulated on the outside. Acycle alternating current feeds the electrodes B which are of oppositep0- larity, and preferably made of steel and so designed and positionedin the furnace that (in the...particula.r case mentioned) a currentdensity of about 90 amperes per square inch at their surface -of contactwith the material will produce the required heat. The solid material tobe treated is introduced continuously at C and the fused prod'- uct inequivalent amount is withdrawn at the overflow D, see Figs. 1 and 2. Theelectrodes B are preferably of circular crosssection and of a diameterdecreasing gradually toward their free or lower ends, as willbeunderstood by the example shown in Fig. 4. This configuration imparts agentleI vtaper to the free end of the electrodes, said taper as shown inFigs. 2, 3 and 4, extendA ing through the major portion of the heatinglength of the electrodes. An electrode of this sha-pe has a fairly'uniform current u density throughout its entire contact are-a.

The operation of the furnace may be started by introducing into thefurnace a. small amount of the material in a fused state, or this smallamount of fused material u l furnace A.

necessary to provide the required conductor between the electrodes maybe produced in situ. This can be done by bringing the electrodes closetogether and in contact with some of the material moistened with alittle water, or by striking an arc momentarily between the electrodesB. As the fusion progresses, the distance between the electrodes isgradually increased until regular normal operating conditions arereached. The drawing does not indicate any particular means for movingthe eelctrodes toward or from each other but any suitable arrangementmay be adopted for this purpose; for instance, the electrodes may bepivoted t0 swing about parallel, horizontal axes, or they may be mountedin holders sliding horizontally toward 'or from each other. Whenelectrodes of proper size and, shape are employed and when the currentconditions are properly adjusted in accordance with the nature of thematerial under treatment, the molten materia-l will be kept insufficiently active circulation by the action of the current, that aproper heat distribution is effected throughout the entire mass of thefused material, and thus a large bath can be maintained in a fusedcondition and at a uniform temperature, without any local overheatingand without any local cooling such as would leave some portions ofthematerial solid.

The circulating liquid can be used as a source of heat, for example, forthe fusion of further quantities of solid material and this is thepreferred procedure used in the\ production of fused` soda ash or sodaashsodium hydroxid mixtures, the solid material being more or lesscontinuously introduced through the chute C into a body of fusedmaterial maintained in a continuous state of fusion and circulation inthe The shape of the furnace proper A is of no particular account andany desired shape may be given to the container or furnace body.

It will be understood, as has been pointed out above, that the minimumcurrent density required depends on the fluidity, viscosity, and othercharacteristics of the fused material and will be different fordifferent materials. If, for example, the substance under treatment issodium carbonate or sodium carbonate with an admixture of sodiumhydroxid up to 30%, satisfactory results are obtained with a currentdensity of from 50 to 100 amperes, and preferably about 90 amperes, ersquare inch at the surface of Contact Orp the electrodes with the fusedmaterial.

The present invention provides a' very convenient and economicalprocedure and means for maintaining relatively large masses of salts orcompounds of similarly poor heat capacity and heat conductivity in afused condition and at a uniform temperature throughout the mass.Moreover, with the present invention, such materials may'be fused on alarge scale and in a con- 70 tinuous manner with a comparatively smallconsumption of current.

In Figs. l and 2, I have also indicated a skimmer rod E located at thesurface of the molten material between the electrodes and the outlet D.This skimmer, which is not an essential part of the apparatus but in.many cases of considerable utility, will prevent unfused material fromreaching theV Overfiow or outlet D. Then employing'o three-phasecurrent, this skimmer E may form one of the three electrodes, the othertwo being formed by the rods B. The fused product, when withdrawn, maybe cast into molds or otherwise disposed of. In cer 35 tain cases, whenit is desired to make a flake product, the material would not bedischarged through the overiow D, but might be lifted out of the bath bymeans of a rotary drum such as indicated at F in Fig. 2, said drumdipping into the bath and picking up continuously a thin layer of moltenmaterial which solidiies as it travels towards the upper part of thedrum. Any suitable means such as a scraper or equivalent device (see GrFig. 5) may be employed for removing the flaky material from such di um.

The apparatus may be varied considerably without departing from thenature of my invention. Fig. 3, for instance, illustrates afunnel-shaped or downwardly contracted container body A', whichconstitutes one of the electrodes of the circuit B, B', the otherelectrode B dipping centrally into the molten muss in substantially thesame manner as described and illustrated with reference to* Figs. l, 2,and 4.

It will be noted that the contact between" the electrodes and the moltenbath is no simply along a limited surface at the very end of theelectrode, but that such contact is all around the periphery of thecurved surface of the electrode dipping into the liquid. This is ofmaterial importance in avoiding a current density so high as to causeinjurious and destructive local effects both upon the electrodes andupon the material under treatment.

In Figs. 5 and 6 the electrodes B are 120 illustrated as arrangedsomewhat differently from the arrangement of electrodes in Figs.

l to 3, In Figs. 5 and 6 one of these electrodes is developed as acurved member whose curved portion is immersed in the bath of fusedmaterial, while the other two electrodes dip into the bath in the formof two separated fingers. In Fig. 5 there are also indicated feedingmeans H for cansinoF travel of solid material into the chute mass, saidmass of the fused mass are less neon7os means I--J for giving the drum Fany desired regulatable sion and means collecting the solidified iakymaterial scraped from the drum F.

This present invention, it Will be observed, requires a eert-ain amountof heat to maintain fusion in the substances under treatment, but also aproper distribution of this heat through the 'various parts of the fusedbeing of relatively poor capacity and heat conductivity. The properdistribution of heat is brought about not by enlarging the electrodes,but rather by restricting thesizc of the electrodes thus apparentlyoperating in the direction of greater local heat concentration andcontrary to the principle of better heat distribution. At the same. timeit has been found, with respect to fused materials of the character inquestion, that by intensifying the current density by restricting thesize of the electrodes` movement will be set up in the fused material toan extent sufficient to cause a proper distribution of heat throughoutthe entire fused mass taken as a Whole and that the fact of thismovement as a. distributor of heat is sufficient to counterbalance theapparently excessive ten'iperature at the electrodes. In other words,Where larger electrodes are used the differences between the temperatureat the electrodes and other parts great but they continue to exist asdifferences and even build up in degree, Whereas when smaller electrodesare used, although the difference in temperature at different parts ofthe mass may be greater than where large electrodes are used, themovement generated in the fused mass is sufficient to bring all parts ofit to more or less the same temperature, continuously thereby avoidingany building up of persisting temperature differences in different partsof the mass of fused material when considered as a whole. The inventioncan be readily applied to materials of various kinds by determining theamount of heat required and then, by reducing one or more of theelectrodes in size until sufficient heat distributive motion is set upin the fused mass to establish a circulation adequate for thedistribution of this heat. As exemplified by the third electrode E ofFigs.

1 and 2 and the electrode B of Fig. 3 it is not necessary for thepractice of my invention that the current density at the contact surfaceof each and all the electrodes should be thus modified.

I claim:

l. In the process of supplying heat to a body of molten material bypassing an electric current through the molten mass, that improvementwhich consists in proportioning the contact area, of an electrode andthe to supply the required heat current so as degree of surfaceimmerlx-L-M for moving and.

while distributing the heat throughout the mass by movements set uptherein and governed by the relation' between the contact area of theelectrode and the current.

2. In the process of supplying heat to a body of molten material bypassing an electric current through the molten mass, that improvementwhich consists in proportioning the contact area of an electrode and thecurrent so ast o supply the requiredheat and at the saine time todistribute the heat sufficiently throughout the massto maintain theentire mass in a continuing condition of fusion, said heat distributionbeing the result of movement set up in the mass suf-- ficiently activeto accomplish the said end, said movement being caused by-the initialproportioning of the contact area of the electrode and the current.

3. The process which comprises establishing a hath of fused material ofpoor heat conductivity, maintaining said bath in continuous `fusionthroughout by passing an electric current therethrough by Way ofelectrodes proportioned with reference to contact area and the currentpassing therethrough to effect by means of the resultant circulatingmotion in the bath a uniform temperature distribution throughout thebath.

4. The process which comprises establishing a bath of fused material ofpoor heat conductivity, maintaining said bath in continuous fusionthroughout by passing an electric current therethrough bywvay ofelectrodes proportioned With reference. to contact area and the currentpassing therethrough to effect by means of the resultant circulatingmotion in the bath a uniform temperature distribution throughout thebath, continuously adding to said ibath and fusing in said bath, whilemaintained in the stated condition, additions of solid material of suchcharacter as, when fused by and in said bath, will become a part of saidbath and effecting withdrawals from said bath, thus augmented, .as thefused material increases, in volume by the fusion of the added solidmaterial.

5. The process Which consists in having the end surface and theperipheral surface of an electrode dip into a mass of fused material,and applying through said electrode a current of a strength sufficientto maintain fusion of the entire mass, and, by proportioning the contactareaof the electrode and the current, bringing about heat distributionthroughout the mass by causing the current to set up motion in the masssufficient t0 maintain the Whole of the mass in a condition ofcontinuous fluidity throughout.

6. In' the process of supplying heat to a body of molten material bypassing an electric current through. the molten mass, that improvementwhich consists in establishingsuch relation between the contact area ofthe electrode and the current. as to Supply the required heat and at thesame time to maintain a continued condition of fluidity throughout themass as the result of movement set up therein by the flow of currenttherethrough.

7. In the process of supplying heat to body of molten material bypassing an electric current through the molten mass, that improvementwhich consists in causing the current in addition to supplying therequired heat to distribute said heat throughout the mass by movementsuflicient to maintain substantially uniform temperature throughout themass.

S. An electric furnace comprising a container for the electrolyte,having an inlet for the raw material and an outletfor the product, anddepending electrodes of downwardly-tapering form in said container',said taper extending throughout the major portion of the heating lengthof the electrode.

9. An electric furnace comprising a container for the electrolyte, adepending electrode of downwardly-tapering forni in said container, thetaper of said electrode extending throughout a major portion of theheating length thereof, and a co-operating electrode.

10. An electric furnace comprising a container for the electrolyte andelectrodes of substantial contact area, means for passing through theelectrolyte a current of suf-A ficient strength to maintain a fusedcondition in the electrolyte, the contact area of the electrode beingrelatively sosmall as to keep the fused mass in motion sufficiently tocause heat distribution'throughout the mass, while relatively so largeas to avoid detrimental over-heating of the eectrodes or portions of theelectrolyte adjacent thereto.

11. An electric furnace comprising a container for the electrolyte,having an inlet for the raw material and an outlet for the product,electrodes located between said in let and said outlet adapted, byreason of their restricted size, to maintain a condition of continuousfluidity in the fused material as the result of motion set up in saidmaterial by the current flowing through said electrodes of restrictedsize, and a skimmer located between said electrodes and said outlet.

l2. An electric furnace con'iprising a container for the electrolyte,having an inlet .for the raw material and an outlet for the product,electrodes in said container adapt ed, by reason of their restrictedsize, to maintain a condition of continuous fluidityT in the fusedmaterial as the result of motion sul; up in said nuiterial by thecurrent flow' ing through said electrodes of restricted size, and askimmer located in the container toward the outlet thereof.

13. An electric furnace comprising a container for the electrolyte,having an inlet for the raw material and an outlet for the product,electrodes in said container adaptA cdby reason of their restrictedsize, to maintain a condition of continuous fluidity in the fusedmaterial as the result of mo tion set up in said material by the currentflowing through said electrodes of restricted size, and a rotary drumfor lifting the fused electro'yte from the container.

14. An electric furnace comprising a container for the electrolyte,having an inlet for the raw material and an outlet for the product,electrodes in said container adapted, by reason of their restrictedsize, to maintain a condition of continuous fluidity in the fusedmaterial as the result of motion set up in said material by the currentflowing through said electrodes of restricted size, and a skimmerlocated in the container toward the outlet thereof, and a rotary drumlocated between said skimmer and the outlet, to lift fused electrolytefrom the container.

15. An electric furnace comprising a container' for the electrolyte,having an inlet for the raw material and an outlet for the product,electrodes in said container adapted, by reason of their restrictedsize, to maintain a condition of continuous fluidity in the fusedmaterial as the result of motion set up in said material by the currentflowing through said electrodes of restricted size, and a rotary drumlocated between said electrodes and the outlet to lift the fusede`cctrolyte from the container.

In testimony whereof I have hereunto set my hand.

CLARENCE T. PATTERSON.

